Method Of Manufacturing A Touch Sensitive Panel

ABSTRACT

A method of manufacturing a transparent conductive film for a touch sensitive panel, comprising: providing a layered structure comprising a plurality of homogeneous layers which include at least a first transparent conductive layer, a second transparent conductive layer, and a transparent support substrate between the first transparent conductive layer and the second transparent conductive layer, the transparent support substrate being the thickest layer of the layered structure; forming an electrode pattern in the first transparent conductive layer by laser ablation of the first transparent layer by a laser beam incident on the first transparent layer from a side of the transparent support substrate on which the first transparent layer is provided; wherein the laser beam and transparent support substrate are configured such that the laser beam energy density is reduced by 50% or more by the transparent support substrate.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 16/978,999 filed Sep. 8, 2020, and claiming priority to U.S.National Phase Application under 35 U.S.C. 371 of InternationalApplication No. PCT/GB2019/050440 filed on Feb. 19, 2019, which claimsthe benefit of priority from Great Britain Patent Application No.1803723.4 filed on Mar. 8, 2018. The entire disclosures of all of theabove applications are incorporated herein by reference.

FIELD

The invention relates to a method of manufacturing a touch sensitivepanel. In particular, the invention relates to a method comprisingforming electrode patterns in a transparent conductive layer by laserablation.

BACKGROUND

Capacitive touch panel technology is in wide use, for example in mobilephones, tablet computers, personal digital assistants, handheld gamesconsoles, satellite navigation systems, and other user interfaceconsoles.

In such devices, an XY array of sensing electrodes is formed in layersof transparent conductive material. In use, capacitance forms betweenthe user's fingers and the projected capacitance from the sensingelectrodes. A touch is made, precisely measured and translated into acommand which is executed by underlying electronic devices for anappropriate software application. Such panels enjoy the benefits ofresponding accurately to both fingers and styli.

One particular form of touch panel technology has two separatedtransparent conducting layers and it is the changes in the mutualcapacitance between the layers at the intersection points of theelectrode arrays that are detected.

The transparent conductive layers are each divided into a plurality ofdiscrete electrode cells which are electrically connected in a firstorthogonal direction but electrically isolated in a second orthogonaldirection. The electrode pattern may be the same for both layers or maybe different.

One method of forming an electrode pattern in the transparent conductivelayers is to use a laser beam to ablate portions of the conductivelayers from the surface of a transparent support substrate. Such amethod provides a higher throughput and it lowers cost than alternativemethods such as chemical etching of the electrode pattern.

Typically, the transparent conductive layers may be formed from indiumtin oxide (ITO) or a nanomaterial comprising metal nanowires, or carbonnanotubes, for example. The transparent support substrate is typicallyformed from a flexible polymer, for example a film of polyethyleneterephthalate (PET). PET is most widely used because it is inexpensiveto produce.

However, forming an electrode pattern in a first transparent conductivelayer using a laser beam can cause damage to a second transparentconductive layer formed on the other side of the substrate to the firsttransparent conductive layer. Various attempts have been made to addressor circumvent this problem.

In one example, the second conductive layer is formed only after theelectrode pattern has been formed in the first conductive layer.However, in this example, throughput is compromised. In another example,the first and second conductive layers are formed from differentmaterials, having different ablation thresholds. However, manufacturingcosts are higher as a result. In another example, lenses are configuredto diverge the laser beam as it passes through the support substrate toreduce the energy density at the far side of the substrate. However,manufacturing costs are higher as a result. In another example, anadditional light blocking layer is added between the conductive layersand the substrate to protect the far-side conductive layer while theelectrode pattern is formed in the near-side conductive layer. However,the touch sensitive panel is thicker and manufacturing costs are higheras a result.

The present invention aims to at least partially address some of theproblems discussed above.

Accordingly, the present invention provides a method of manufacturing atouch sensitive panel, comprising: providing a layered structurecomprising a plurality of homogeneous layers which include at least afirst transparent conductive layer, a second transparent conductivelayer, and a transparent support substrate between the first transparentconductive layer and the second transparent conductive layer, thetransparent support substrate being the thickest layer of the layeredstructure; forming an electrode pattern in the first transparentconductive layer by laser ablation of the first transparent layer by alaser beam incident on the first transparent layer from a side of thetransparent support substrate on which the first transparent layer isprovided; wherein the laser beam and transparent support substrate areconfigured such that the laser beam energy density is reduced by 50% ormore by the transparent support substrate.

By selecting the laser and the material of the transparent supportsubstrate in accordance with the invention, the transparent supportsubstrate itself can be used to absorb and/or diffuse laser energy insuch a way as to prevent damage to the second transparent conductivelayer, while the electrode pattern is formed in the first conductivetransparent layer. Such a manufacturing method does not requireadditional layers or additional different materials for the layers.Accordingly, the method is relative inexpensive, is able maintain a highthroughput and produces a relatively thin touch panel.

The laser beam may have a wavelength of from 200 nm to 400 nm, forexample 266 nm or 355 nm. Such laser beams can be produced relativelyinexpensively and reliably, for example using diode-pumped solid statelaser devices.

The transparent support substrate may be formed from a materialcomprising one of colourless polyimide (CPI), polyetherimide (PEI),polyether ether ketone (PEEK), polycarbonate (PC) and PET. Thetransparent support substrate may be formed from a material comprisingat least 90% by weight of one of CPI, PEI, PC, PEEK and PET. Thetransparent transport substrate may consist essentially of one of CPI,PEI, PC, PEEK and PET. CPI, PEI and PEEK have desirable absorptioncharacteristics in a wavelength range around 355 nm. PET and PC havedesirable absorption characteristics in a wavelength range around 266nm.

The present invention also provides a transparent conductive film for atouch sensitive panel, having a layered structure comprising: aplurality of homogenous layers which include at least a firsttransparent conductive layer, a second transparent conductive layer, anda transparent support substrate between the first transparent conductivelayer and the second transparent conductive layer, the transparentsupport substrate being the thickest layer of the layered structure;wherein the transparent support layer is formed from a materialcomprising one of CPI, PEI, PC and PEEK.

BRIEF DISCRIPTION OF THE DRAWINGS

Further features and advantages of the invention will be described belowby way of non-limiting examples, together with the accompanyingdrawings, in which:

FIG. 1 schematically shows an example transparent conductive film for atouch sensitive panel;

FIG. 2 schematically shows an example transparent conductive film for atouch sensitive panel; and

FIGS. 3A and 3B show example electrode patterns formed in first andsecond transparent conductive layers;

FIG. 4 schematically shows an example apparatus for carrying out themethod of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 shows a cross-section through a transparent conductive film for atouch sensitive panel. The transparent conductive film comprises alayered structure comprising a plurality of homogenous layers. As shownin FIG. 1 these layers may comprise a first transparent conductive layer2, a second transparent conductive layer 3, and a transparent supportsubstrate 1 between the first transparent conductive layer 2 and thesecond transparent conductive layer 3. The transparent support substrate1 provides stability to the transparent conductive film. Accordingly, itis the thickest layer in the film. The transparent support substrate 1may account for 50% or more, or 75% or more, of the thickness of thetransparent conductive film, for example.

Further layers may be provided. For example, as shown in FIG. 2, anadditional adhesive layer 4 may be provided between the transparentsupport substrate 1 and the transparent conductive layers 2,3 in orderto improve adhesion of the transparent conductive layers 2, 3 to thetransparent support substrate 1. The adhesive layers 4 may be provideddirectly between the transparent conductive layers 2, 3 and thetransparent support substrate 1, respectively. In other words, theadhesive layers may contact both the transparent conductive layers 2, 3and the transparent support substrate 1, respectively. However, theadhesive layers 4 are not required, they are optional. For example, thetransparent conductive layers 2, 3 may be provided directly on oppositesurfaces of the transparent support substrate 1, as shown in FIG. 1.

The transparent support substrate 1 is transparent to visible light andmay be electrically insulating. The transparent support substrate 1 maybe rigid or may be flexible. The transparent support substrate 1 may bemade of a polymer material, for example. Such materials include PET,CPI, PEI, PC and PEEK. The thickness of the transparent supportsubstrate 1 may be less than 1 mm. For example, the transparent supportsubstrate 1 may be at least 0.01 mm thick and/or less than 0.15 mmthick. The transparent support substrate 1 may be around 0.05 mm thick,for example. A thinner support substrate 1 make a more flexible film.However, if the transparent support substrate 1 becomes too thin, it isdifficult to handle.

The first and second transparent conductive layers 2, 3 may be formedfrom an inorganic oxide material such as indium tin oxide (ITO), tinoxide (SnO2), zinc oxide (ZnO), or other transparent conductive oxides(such as fluorine doped tin oxide (FTO)). Such materials may be appliedby physical vapour deposition, for example. However, other methods mayalso be used. Other materials may be used for the transparent conductivelayers, for example nano particle materials. Nano-particle materials mayinclude metal nanowires (e.g. silver nanowires, AgNW), carbon nanotubes(CNT), carbon nanobuds (CNB), or graphene, for example. Suchnanoparticle materials may be applied by printing onto the substrate 1or by a transfer film. The first and second transparent conductivelayers 2, 3 may have a thickness of from 30 nm to 300 nm. The sheetresistances of the transparent conductive layers 2, 3 may be from 10ohms/square to 30 ohms/square.

The transparent support substrate 1 and the transparent conductivelayers 2, 3 may respectively and/or in combination have an opticaltransmission in the visible wavelength range of at least 85%, or atleast 90%.

FIGS. 3A and 3B respectively show example electrode patterns formed inthe first and second transparent conductive layers 2, 3. These Figuresshow plan views of opposite faces of the transparent conductive film.The electrodes patterns formed in each of the transparent conductivelayers 2, 3 comprise parallel lines. These parallel lines are orthogonaland form transmit electrodes (TX), and receive electrodes (RX).Alternatively, different electrode patterns may be formed in the firstand second transparent conductive layers 2, 3.

The electrode patterns may be formed by laser ablation of thetransparent conductive layers 2, 3 by a laser beam 5. As shown in FIG.1, a laser beam 5 may be incident on the first transparent conductivelayer 2 from a side of the transparent support substrate 1 on which thefirst transparent layer 2 is provided. Further, a laser beam 5 may beincident on the second transparent conductive layer 3 from a side of thetransparent support substrate 1 on which the second transparentconductive layer 3 is provided. Also as shown in FIG. 1, the formationof the electrode patterns in the first transparent conductive layer 2and the second transparent conductive layer 3 may be performedsimultaneously.

The electrode patterns are formed by laser ablation of the transparentconductive layers 2, 3. In other words, the laser beam 5 breaks the bondbetween the transparent conductive layers 2, 3 and the substrate 1. Thetransparent conductive layers 2, 3 may have a laser ablation thresholdenergy density of from 0.5 J per cm2 to 1 J per cm2, for example.

The laser beam 5 may have an ultraviolet (UV) wavelength. For example,the laser beam wavelength may be between 200 nm and 400 nm. The laserbeam wavelength may be between 200 nm and 300 nm, or alternativelybetween 300 nm and 400 nm. For example, the laser beam wavelength may be266 nm or 355 nm. The laser beam 5 may be produced by a diode-pumpedsolid state laser, for example. The laser beam 5 may be pulsed. Theenergy density of the laser beam 5, within the transparent conductivelayer 2, 3 being processed, or at an interface between the transparentconductive layer 2, 3 and an adjacent layer, may be equal to or greaterthan the laser ablation threshold of the transparent conductive layers2, 3. In other words, the energy density of the laser beam 5 may be offrom 0.5 J per cm2 to 1 J per cm2, or higher, for example. Opticalelements, e.g. lenses and/or mirrors may be used to focus the laserbeams 5. The laser beam 5 may be focused at the side of the transparentconductive layers 2, 3 furthest from the laser beam 5.

The transparent support substrate 1 is configured such that the laserbeam energy density is reduced by 50% or more by the transparent supportsubstrate 1. The laser beam energy density may be reduced by 75% or moreby the transparent support substrate 1. In other words, the material andthickness of the transparent support substrate is such that 50% or moreof the laser energy is absorbed by the transparent support substrate 1.The transparent support substrate material and thickness, and the laserwavelength and energy density may be mutually selected such that duringlaser ablation, the laser beam energy density is reduced by 50% or moreby the transparent support substrate 1.

The transparent support substrate 1 may be formed from a polymericmaterial which, having a thickness of from 0.01 mm to 0.15 mm, absorbs50% or more of laser energy incident thereon having a wavelength of from200 nm to 400 nm and an energy density sufficient to ablate anconductive layer (e.g. 0.5 J per cm2 to 1 J per cm2 or higher) andtransmits at 90% or more of visible light incident thereon.

In one embodiment of the present invention, a 355 nm laser is used toform the electrode pattern and the transparent support substrate 1 isformed from CPI and has a thickness of around 0.05 mm. CPI has arelatively high absorption at 355 nm. Therefore, the laser beam energydensity is reduced by more than 50% as the laser beam 5 passes throughthe transparent support substrate 1. PEI, PC and PEEK are also suitablesubstrate materials for use with a 355 nm laser and may be substituted.

In another embodiment of the present invention, a 266 nm laser is usedto form the electrode pattern and the transparent support substrate 1 isformed from PET and has a thickness of around 0.05 mm. PET has arelatively high absorption at 266 nm. Therefore, the laser beam energydensity is reduced by more than 50% as the laser beam 5 passes throughthe transparent support substrate 1. PC is also suitable substratematerial for use with a 266 nm laser and may be substituted.

Until now, CPI, PEI, PC or PEEK have not been considered for use as asubstrate material in touch sensitive panels. PET is the preferredsubstrate material for touch sensitive panels. However, the inventorshave found that CPI, PEI, PC and PEEK have the surprising effect ofefficiently absorbing laser radiation in a wavelength range including355 nm, while being sufficiently transparent at visible wavelengths.

Further, until now, PET has not been considered for use as a substratematerial in touch sensitive panels together with an electrode formingmethod using a UV laser wavelength without additional blocking layersbeing provided on the substrate. However, the inventors have found thatPET has the surprising effect of efficiently absorbing laser radiationin a wavelength range including 266 nm. Accordingly, a PET substrate canbe used without the need for a blocking layer, if used in combinationwith an appropriate laser wavelength.

FIG. 4 shows an example apparatus 10 for manufacturing the transparentconductive film of the invention. The transparent conductive film,including the first and second transparent conductive layers 2, 3 on thetransparent support substrate 1 are provided on a first reel 11. Thetransparent conductive film is unwound from the first reel 11 and thensubjected to the laser beams 5 to form the electrode patterns. Thetransparent conductive film with the electrode patterns formed thereonmay be rewound onto a second reel 12.

As shown in FIG. 4, the apparatus 10 may further comprise drivingrollers 13 for driving the transparent conductive film through theapparatus, i.e. from the first reel 11 to the second reel 12. In theexample apparatus shown, three pairs of driving rollers 13 a, 13 b and13 c are provided. The first and seconds reels 11, 12 may also bedriven.

The apparatus 10 may further comprise at least one tension pickup 15. Inthe example apparatus 10 shown in FIG. 4, two tension pickups 15 a, 15 bare provided, one adjacent the first reel 11 and the other adjacent thesecond reel 12. The tension pickups 15 are configured to adjust thetension of the transparent conductive film by pressing on thetransparent conductive film with a given pressure.

The apparatus 10 may further comprise a cleaning unit 17, downstream ofthe laser beams 5, for cleaning the transparent conductive film ofdebris resulting from the laser ablation process, before the transparentconductive film is rewound onto the second reel 12. The cleaning unit 17may eject a stream of gas, such as air, onto the transparent conductivefilm to clean it.

The apparatus 10 may further comprise film protection units 15. Forexample, as shown in FIG. 4, two film protection units 15 a, 15 b may beprovided, one adjacent the first reel 11 and the other adjacent thesecond reel 12. The protection units 15 a, 15 b protect the film as itunwinds and rewinds.

The apparatus 10 may further comprise additional rollers 16 for changingthe direction of travel of the transparent conductive film between thefirst reel 11 and the second reel 12.

It may be advantageous to unwind the transparent conductive film fromthe first reel 11 and rewind the transparent conductive film onto thesecond reel 12 in a substantially horizontal direction in order toreduce tension on the transparent conductive film. However, it may alsobe advantageous to form the electrode patterns while the transparentconductive film is substantially vertical. This is in order to preventsagging of the transparent conductive film, which may reduce theaccuracy of the electrode patterning process. Accordingly, a firstroller 16 a may be provided between the first reel 11 and the laser beam5 to change the direction of the transparent conductive reel fromsubstantially horizontal to substantially vertical. Further, a secondroller 16 b may be provided between the laser beam 5 and the second reel12 to change the direction of the transparent conductive film fromsubstantially vertical back to substantially horizontal.

Additional rollers 16 d and 16 e may be provided between the secondroller 16 b and the second reel 12 in order to reduce the overall lengthof the apparatus 10 in the horizontal direction, for example in order toaccommodate the cleaning unit 17, as shown in FIG. 4.

When forming the electrode pattern, the transparent support substrate 1may be driven relative to the laser beam 5 in a sub-scanning direction(direction up/down the page in FIG. 4) and the laser beam 5 may bedriven relative to the transparent support substrate 1 in amain-scanning direction (direction into/out of the page in FIG. 4).

1. A method of manufacturing a transparent conductive film for a touchsensitive panel, comprising: providing a layered structure comprising aplurality of homogeneous layers which include at least a firsttransparent conductive layer, a second transparent conductive layer, anda transparent support substrate between the first transparent conductivelayer and the second transparent conductive layer, the transparentsupport substrate being the thickest layer of the layered structure;forming an electrode pattern in the first transparent conductive layerby laser ablation of the first transparent layer by a laser beamincident on the first transparent layer from a side of the transparentsupport substrate on which the first transparent layer is provided;wherein the laser beam and transparent support substrate are configuredsuch that during laser ablation, the material and thickness of thetransparent support substrate are such that the laser beam energydensity is reduced by 75% or more by absorption by the transparentsupport substrate.
 2. The method of claim 1, further comprising: formingan electrode pattern in the second transparent conductive layer by laserablation of the second transparent layer by a laser beam incident on thesecond transparent layer from a side of the transparent supportsubstrate on which the second transparent layer is provided.
 3. Themethod of claim 2, wherein the steps of forming the electrode pattern inthe first transparent conductive layer and forming the electrode patternin the second transparent conductive layer are performed simultaneously.4. The method of claim 1, wherein the wavelength of the laser beam isultraviolet.
 5. The method of claim 4, wherein the wavelength of thelaser beam is from 300 nm to 400 nm.
 6. The method of claim 5, whereinthe wavelength of the laser beam is 355 nm.
 7. The method of claim 5,wherein the transparent support substrate comprises one of CPI, PEI andPEEK.
 8. The method of claim 3, wherein the wavelength of the laser beamis from 200 nm to 300 nm.
 9. The method of claim 8, wherein thewavelength of the laser beam is 266 nm.
 10. The method of claim 8,wherein the transparent support substrate comprises one of PET and PC.11. The method of claim 1, wherein the laser beam is produced by adiode-pumped solid state laser.
 12. The method of claim 1, wherein theenergy density of the laser beam at the surface of the substrate is from0.5 Jcm⁻² to 1 Jcm⁻².
 13. The method of claim 1, wherein the thicknessof the transparent support substrate is from 0.01 mm to 0.15 mm.
 14. Themethod of claim 1, wherein the first and/or second transparentconductive layers are formed from ITO.
 15. The method of claim 1,wherein the first and/or second transparent conductive layers are formedfrom nanowires, carbon nanotubes or carbon nanobuds.
 16. The method ofclaim 1, wherein the first and/or second transparent conductive layershave an ablation threshold of from 0.5 Jcm⁻² to 1 Jcm⁻².
 17. The methodof claim 1, wherein the first and/or second transparent conductivelayers are attached directly to the transparent support substrate. 18.The method of claim 1, wherein the first and/or second transparentconductive layers are attached to the transparent support substrate by atransparent adhesive layer.
 19. The method of claim 1, wherein the firstand/or second transparent conductive layers have a thickness of between30nm and 300nm.
 20. The method of claim 1, wherein the layered structureis unwound from a first reel prior to forming to the electrode pattern.21. The method of claim 1, wherein the layered structure is wound onto asecond reel after forming the electrode pattern.
 22. The method of claim1, wherein in the step of forming the electrode pattern, the transparentsupport substrate is driven relative to the laser beam in a sub-scanningdirection and the laser beam is driven relative to the transparentsupport substrate in a main-scanning direction.
 23. The method of claim22, wherein the sub-scanning direction is substantially vertical.
 24. Atransparent conductive film for a touch sensitive panel, having alayered structure comprising: a plurality of homogenous layers whichinclude at least a first transparent conductive layer, a secondtransparent conductive layer, and a transparent support substratebetween the first transparent conductive layer and the secondtransparent conductive layer, the transparent support substrate beingthe thickest layer of the layered structure; wherein the transparentsupport layer comprises one of CPI, PEI, and PEEK.